fixed swagger message issue

components/device-mgt/org.wso2.carbon.device.mgt.api/src/main/java/org/wso2/carbon/device/mgt/jaxrs/api/DeviceNotification.java

@@ -112,7 +112,7 @@ public interface DeviceNotification {
             value = "Sending a Device Notification",
             notes = "Notify users on device operation failures and other information using this REST API")
     @ApiResponses(value = {
-            @ApiResponse(code = 201, message = "NNotification has added successfully"),
+            @ApiResponse(code = 201, message = "Notification has been added successfully"),
             @ApiResponse(code = 500, message = "Error occurred while updating notification status")
     })
     @Permission(scope = "device-notification-modify",

components/device-mgt/org.wso2.carbon.device.mgt.api/src/main/java/org/wso2/carbon/device/mgt/jaxrs/api/impl/DeviceNotificationImpl.java

@@ -97,7 +97,7 @@ public class DeviceNotificationImpl implements DeviceNotification{
         ResponsePayload responseMsg = new ResponsePayload();
         try {
             DeviceMgtAPIUtils.getNotificationManagementService().addNotification(notification);
-            responseMsg.setMessageFromServer("Notification has added successfully.");
+            responseMsg.setMessageFromServer("Notification has been added successfully.");
 			responseMsg.setStatusCode(HttpStatus.SC_CREATED);
             return Response.status(Response.Status.CREATED).entity(responseMsg).build();
         } catch (NotificationManagementException e) {